Solid-state image sensors which produce image data by photoelectrically converting light have been used in imaging devices since the past. A differential amplification-type image sensor that amplifies differential signals using a pair of transistors for the purpose of increasing sensitivity, for example, has been proposed (e.g., refer to Patent Literature 1). Such a differential amplification-type solid-state image sensor has unit pixels from which pixel signals are read and dummy pixels from which no signals are read arranged therein. In addition, a readout circuit included in the solid-state image sensor reads pixel signals differentially amplified by a differential pair formed by an amplifier transistor included in a unit pixel and an amplifier transistor included in a dummy pixel and performs a correlated double sampling (CDS) process thereon.
Here, the CDS process is a process of reducing fixed-pattern noise by reading signals from pixels twice and obtaining a difference between levels of the signals as pixel data. The level of signals read the first time is called a P-phase level and the level of signals read the second time is called a D-phase level.